In the manufacture of integrated circuit devices, printed circuit boards, printing plates, and in related arts, resist processes are used whereby photochemical images are formed on a substrate to protect selected portions of the substrate during subsequent manufacturing processes such as, for example, etching, metal deposition, and diffusion processes. The resist processes employ radiation sensitive organic compositions which are coated onto the substrate surface and then exposed patternwise to light or other suitable actinic radiation such as, for example, x-rays, gamma rays, or an electron beam. The exposed resist layer is then developed by methods known in the art and the portions of the substrate which are bared by development can then be treated.
Both positive and negative working photoresists are known. A positive resist is composed typically of a base-soluble binder such as a phenol-formaldehyde novolak resin and a sensitizer, that is, a photoactive compound, such as a diazo compound. Such sensitizers and resists are described, for example, in U.S. Pat. Nos. 3,046,118; 3,046,121; 3,106,465; 3,201,239; 3,666,473; 4,009,033 and 4,093,461 which are each incorporated herein by reference.
In manufacturing processes employing photoresists, the rate of production is dependent upon the time required to form the photomechanical image which, in turn, depends in part on the time required to expose the resist to the necessary amount of activating radiation and on the time required to then develop the latent image-bearing resist. Accordingly, four interrelated factors determine the rate of product through-put: radiation intensity and exposure time, and developing solution concentration and solution contact time.
Typically, exposed resists will dissolve in developer solution of a given concentration at a certain rate. This is true whether development is by immersion or by puddle or spray techniques. Generally, solution contact time is pre-set. The minimum necessary exposure time to achieve complete development of the photoresist is then determined, often by trial and error. Underexposure of the photoresist generally cannot be effectively off-set by using developing solution above the recommended concentration since this normally will result in significant loss of selectivity. That is, a greater portion of unexposed resist will be dissolved along with the exposed portion. Consequently, there is a disadvantageous loss of resolution in the photomechanical image and, therefore, in the quality of the subsequently treated image. Accordingly, in a typical manufacturing process employing a source of actinic radiation of certain intensity, the proper exposure time is determined by first setting the time longer than necessary and decreasing it incrementally until the photomechanical image is just developed during the pre-set solution contact time. Thus, for example, where development is by immersion for 60 seconds in a developing solution, the exposure time is adjusted downward until development is just completed in the 60 second immersion time.
A significant disadvantage inherent in the use of known developers relates to metal ion contamination of the work piece, especially integrated circuit devices and the like. The ever smaller lines and spaces being used for the circuitry of such devices make it necessary that there be no contamination by current carrying metal ions, since the functional properties of the device could be affected.
Known developers comprise metal ions and thus can cause metal ion contamination. Inadequate rinsing of the device after development of the photomechanical image can result in metal ion contamination and this is especially troublesome with automatic in-line developing methods, in which there is no immersion rinse. Metal ion contamination can cause failure of finished IC devices.